Set Appliance State:

Gas Off
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
On/Off Switch in ON position
Mode Selector Switch to Summer
Water Thermostat to MAX
Connect a U-Gauge to the Gas Valve outlet pressure point
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

With the boiler alight for approximately one minute, slowly turn the DHW Thermostat to minimum.
Does the burner flame reduce to a low rate of approximately 1.7mbar?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.